The present invention relates to a perfecting printer such as a laser printer or the like, and more particularly, to a perfecting printer having a control unit for controlling a double-face printing operation thereof.
As disclosed in Japanese Laid-Open Patent Publication No. 59(1984)-179354, there has been already known a perfecting printer such as a laser printer in which data such as character data, graphic data or the like can be printed on both the obverse and reverse faces of a sheet. In order to print such data on both of the faces of the sheet (that is, to perform a double-face printing or a perfecting printing operation, the following operation has been generally adopted in the conventional perfecting printer: Print data to be printed on both of obverse and reverse faces of one or more sheets, which are transferred from a host computer or the like, are stored through an input buffer into a storage area in a page memory of the perfecting printer and then converted into an image data represented by a binary digit in a video RAM, thereafter perfecting a printing operation based on the image data.
In the perfecting printer as described above, almost the entire storage area of the page memory is almost used to store the print data, and therefore there occurs a possibility that the page memory runs out of any empty area capable of storing the print data therein, that is, the page memory becomes full of a part of the print data to be stored before a process of storing all of the print data for plural sheets having double-face pages into the page memory is completed, (hereunder referred to as "memory-full state").
If the perfecting printer adopts a face-down discharge operation in which a printed sheet is discharged with its obverse face down, it is required that an image is printed first on the reverse face of the sheet, and then on its obverse face. Accordingly, in order to perform the face-down discharge operation in the perfecting printer, it is required to entirely store the print data for double faces of a sheet in the page memory.
In the conventional perfecting printer, if the memory-full state occurs in the page memory during the storing operation of the print data into the page memory, a control unit, which is generally provided in the perfecting printer, recognizes the memory-full state as a memory-full error, interrupts any subsequent operations for storing and printing the print data, and waits for an instruction from an operator. In accordance with indication of the memory-full error, the operator clears the page memory and then selects a one-page printing mode (a single-face printing mode) to retransmit the print data for the single face of the sheet from the host computer to the perfecting printer. Therefore, the memory-full state of the page memory lowers the throughput of the printing device.